Reducing the quantity of water in formulations containing hydraulic binders, though without altering their fluidity, is essential: this results in doping their mechanical properties. To do so, the person skilled in the prior art has for several years developed additives known as “water-reducing agents”, also known by the expressions “plasticizing agents”, “plasticizers”, and “superplasticizers”.
Historically, the first of them were lignosulfonates, as described in the document U.S. Pat. No. 3,772,045. Polycondensates of formaldehyde and naphtalene or melamine sulfonates were then used, as illustrated in the documents U.S. Pat. No. 3,359,225 and U.S. Pat. No. 4,258,790.
Once adsorbed onto the surface of the cement particles, these negatively charged polymers cause an electrostatic repulsion phenomenon, which is the cause of the cement particles' dispersion mechanism; in particular, the document “Superplasticizers for extending workability” (International Conference on superplasticizers and other chemical additives in concrete, Sorrento Italy, Oct. 29-Nov. 1, 2006, supplementary paper, Publ. Malhotra, American Concrete Institute, pp. 263-277) may be consulted.
A new better-performing family of water-reducing agents then appeared: that of carboxylic comb-branched polymers with a skeleton that is generally (meth)acrylic in nature, onto which are grafted side-chains terminated by hydrophilic groups. The molecular weight of these agents varies between about 10,000 and 100,000 g/mol, the molecular weight of the lateral oxyalkylated group being between 1,000 and 10,000 g/mol: in these domains, better-performing agents in terms of plasticizers are obtained.
This improved water-reducing power is explained by the existence of a steric repulsion mechanism relating to the presence of the side-chains, in combination with the electrostatic repulsion phenomenon caused by the anionic carboxylic groups. There are currently 2 types of technologies for accessing these polymers, which respectively lead to an end product in liquid or solid form.
The solid products are powders obtained through adsorption/drying the comb-branched polymer onto the surface of a solid substrates such as a silicon particle (see the document EP 1,636,280), by synthesizing the main chain, drying and then functionalizing it with molten macromonomers (see documents FR 2,900,930 and FR 2,926,558), or simply by drying said comb-branched polymer (see documents EP 1,052,232 and WO 00/17263). Besides the fact that the step of drying is very energy-consuming, the dry and powdered form of these products makes them difficult to work and particularly to transfer from one container to another (by definition, these products cannot be pumped). The products Mighty™ 21 PSN and Melflux™ 1641 F are examples of such polymers sold in the form of powders, respectively by the companies Kao Chemicals™ and BASF™.
Liquid products are obtained by direct copolymerization of monomers in a majority-aqueous environment, according to methods described in the documents JP 08-217505, GB 2,319 522, EP 1,136,507, EP 1,179,517, EP 1,218,427 and EP 1,789,462. Polymers in a solution in water are thereby obtained, whose liquidity is sought to be prioritized. The Applicant is using the term “liquidity” to designate the product's capacity to be workable and particularly pumpable. This ability is directly measurable via the Brookfield™ viscosity value of the obtained polymer solution, measured at 25° C. and at 100 revolutions per minute (Bk 100) for a given solids content (SC) expressed as a % by dry weight of polymer compared to the total weight of said solution. For a given solids content, the product is more liquid the lower this Brookfield™ viscosity value is.
However, the liquid products currently accessible on the market exhibiting solids contents between 25% and 60% particularly include:                Nopco™ SPC-100 (SC=40%, Bk100=400 mPa·s) from the company NOPCO™;        Nopcoflow™ WR-400S (SC=50%, Bk100=300 mPa·s) from the same company;        Nopcoflow™ WR-460 (SC=50%, Bk100=600 mPa·s) from the same company;        the line of products CP-WRM, CP-WB, CP-RS, CP-ST, CP-HR (SC=40%, Bk100<300 mPa·s) from the company LG Chem™;        the Powerflow™ line of products (SC=45%, Bk100=500 mPa·s) from the company KG Chemicals™;all of these characteristics are given on said products' fact sheets, which are themselves accessible on the corresponding companies' websites.        
Additionally, the syntheses of liquid comb-branched polymers described in the literature always imply a quantity of water such that the end solids content of products may not exceed 60% of their total weight. This solids content may be increased artificially by means of formulation additives, such as surface active agents or solvents whose function is to improve the solubility of said comb-branched polymer in water. That said, using such additives constitutes an additional step of fabrication, and complicates the resulting formula. Additionally, some of them (particularly including solvents) constitute dangers for the formulator and the environment. Finally, these additives play no part in the plasticizing power of the end product.
Currently, it is not known how to manufacture comb-branched polymer solutions which are sufficiently liquid to be workable given commercially very advantageous solids content levels, particularly those above 60%, or even 80%, or even 95% of their total weight either without implementing, or while considerably reducing the quantity of, surface active agents or solvents. Reduced quantity refers to a % by mass of solvents or surface active agents less than 5%, more preferably 2%, most preferably 1% of the total weight of the comb-branched polymer formulation.
In view of this, the inventors have now developed the use, in a method for manufacturing an aqueous solution of a (meth)acrylic comb-branched polymer functionalized by side-chains of the alcoxy- or hydroxy-polyalkylene glycol type, and as an agent having the function of improving the fluidity of said solution, of at least one alcoxy- or hydroxy-polyalkylene glycol polymer with the formula (I):R-(EO)-(PO)-R′  (I)                EO and PO respectively designate ethylene oxide and propylene oxide,        R designates a polymerizable unsaturated function,        R′ represents hydrogen or an alkyl group having 1 to 4 carbon atoms, and more preferably hydrogen,said macromonomer being characterized:        in that it exhibits a molecular weight of between 1,000 g/mol and 10,000 g/mol, more preferably between 2,000 and 6,000 g/mol,        and in that the % by mass of the PO group compared to the total mass of the EO and PO groups is between 15% and 95%, more preferably between 20% and 90%, more preferably between 50% and 90%.        
Surprisingly, as it was neither disclosed nor suggested in the state of the art, the particular choice of the level of propylene oxide units leads to comb-branched polymer solutions that exhibit improved pumpability and workability compared to the comb-branched polymer solutions of the prior art. In concrete terms, for a given molecular weight of the monomer with formula (I), the full benefit of choosing the propylene oxide level in the aforementioned range is proven.
For significant doses by mass of propylene oxide, and for certain molecular weights of the monomer with formula (I), manufacturing aqueous solutions whose solids content is greater than 95% of their weight can even be achieved, while retaining an entirely acceptable workability (as measured via their Brookfield™ viscosity at 25° C. and 100 revolutions per minute). Furthermore, the plasticizing power of such products is not altered.